As medical imaging technology has increased in sophistication and accessibility over the past decade, it is little wonder that the number of scans has also been on the rise.

Conflicting reports have emerged about whether these additional tests are having a commensurate impact on diagnosis—and cure—rates. In fact, a new study shows that for life-threatening injuries, a threefold increase in the number of computed tomography (CT) and magnetic resonance imaging (MRI) scans in emergency rooms has not resulted in an improvement in useful diagnosis.

On the ground, in hospital wards, however, doctors know that the scans can quickly help them see things that other tests cannot. "These CAT scans are way better than the x-rays," says Frederick Korley, an assistant professor of emergency medicine at Johns Hopkins University School of Medicine and co-author of the new study. New CT scans can offer rapid and detailed information about a patient that extensive x-rays, physical examination and observation are often hard-pressed and slower to reveal.

Although Korley and his colleagues had expected to find an increase in the use of these advanced imaging scans in 2007 than in 1998, "the increase was definitely more than we had anticipated," he says. Their study, which was published online October 5 in JAMA The Journal of the American Medical Association, analyzed nationwide hospital data sampled 65,376 injury-related emergency room (ER) visits between 1998 and 2007.

The researchers found that in 1998 a person admitted to an emergency department with an injury had about a 6 percent chance of having a CT or MRI scan. In 2007 that number had jumped to 15 percent. Life-threatening conditions were uncovered by these scans in 1.7 percent of the sampled 1998 ER visits and about two percent of those sampled in 2007. The most dramatic usage increase occurred between 2003 and 2007, during which time the percentage of injured patients who received CT or MRI scans almost doubled.

"It is concerning," Korley says of the trend, but simply based on their analysis, he says, it is not clear that the current imaging rate constitutes "an overuse" of the technology.

Other researchers who have been following and working in the field were not surprised by the study's results. Joshua Broder, an associate professor of emergency medicine at the Duke University Medical Center who was not involved in the new research, is also "worried about the trend," he says.

Many observers, he notes, see these large increases in diagnostic imaging and say, "'What the heck are these people doing? They're just scanning everybody,'" Broder notes. But the view from the inside is much more complicated.
Doctors' dilemmas
When an emergency physician faces a patient with severe and possibly life-threatening injuries, that doctor often needs to make speedy decisions about what tests to order.

"Not every single person needs a test," Korley says of the scans. But with scaling back on detailed imaging tests "will come a potential small miss rate."

Some severe injuries, such as a crushed aorta, will likely be missed by x-rays and physical examinations. Although many of these instances, including aortic injuries, are rare, trauma patients who have them—usually as a result of a rapid deceleration injury, such as car crash or large fall—face a high chance of dying if the condition is not rapidly diagnosed. And just the possibility of discovering such an otherwise hard-to-find but severe internal injury, Broder says, is often enough to prompt a physician to order scans.

"One of the main motivators for doing all those scans is to hunt for that needle in the haystack," he says. "No physician wants their patient to die because they didn't find an injury." And aside from ethical and moral concerns, he notes, underdiagnosis is "a significant source of liability."

Broder, who works and trains residents in trauma medicine, says that his research has led him to look for ways to reduce the growing tendency to test as many patients as possible. But when faced with a severely traumatic patient, he says, "I find myself scanning people because I find myself uncertain if they have an injury." Afterward, if the scan does not reveal any additional injuries, the test will seem unnecessary. "The 'retrospectroscope' is very strong," Broder says, leading doctors and researchers to view many scans as excessive in hindsight—even if in the crush of the moment it seemed worth getting, just to make sure.

Physicians' guidelines for deciding when to order scans are already in place, but just how much doctors follow them is fuzzy. "We need to make sure we're actually applying what we know," Broder says.

In the future more refined scanning technology with lower standard radiation doses, along with decision-support software, might help researchers know what patients are the best candidates for CT or MRI scans—and protect patients who do undergo scanning.

Those who work in the field, however, do not see an easy way out of the dilemma anytime soon. "There's always going to be a ratio of the harm that's produced by performing imaging versus the benefit of the injuries that are detected," Broder says.

Radiation risks, rare rewards
One of the big questions now weighing on doctors is whether they should be subjecting their patients to the scans' radiation, which has been linked to an increased risk of cancer. Although physician awareness of patient radiation exposure was low just six years ago, several high-profile incidents of radiation overdoses from CT scans have increased doctors' deliberations about ordering scans.

"It's very hard to wrap your head around risk," Broder says. And understanding medical imaging radiation exposure risk is still somewhat of an inexact science. Korley explains that some estimates reach back to studies of radiation from the atomic bomb. Other more recent research, including two 2009 studies published in Annals of Internal Medicine, strive to put numbers on the additional numbers of cancers that might be caused by scans. One study estimated that CT scans completed in the U.S. in 2007 will lead to an additional 29,000 cases of cancer.

Whole population risk estimates, however, can conjure "a gross simplification of a very complicated topic," Broder says. When spread across a large population more scans will lead to "basically a guaranteed increase risk of cancer," Broder notes. But on an individual level, a scan might lead to "just a fraction of a percent increase on your baseline cancer risk." A second 2009 study found that about 0.004 percent of women (and about 0.002 percent of men) who got a CT scan to examine their coronary arteries at age 40 would develop cancer because of the test's radiation exposure.

Given a person's high overall risk of dying from cancer (estimates vary from one in seven to one in four), "the individual patient, logically, should always choose to undergo the scan," Broder concludes. So even if a doctor thinks there might be just a 1 percent chance a patient has an aortic injury, the risk of death from that going undiagnosed is some seven to 15 times greater than those projected for developing cancer from a CT scan to look for it, he notes.

Even though these risks are relatively small, however, the researchers concluded in their paper, they are "not trivial." This could be especially true for younger patients, who face a greater jump in cancer risk from radiation exposure than do older patients. People under 45 also make up some 70 percent of patients admitted to ERs for injuries, making them more likely to receive the bulk of imaging scans. And the youngest patients, under the age of 18, were more than twice as likely to get CT or MRI scans in 2007 as they had been in 1998 (9.1 percent versus 4.4 percent).

Aside from any potential radiation exposure risk, the scans can be costly, in terms of money as well as time and resources. Visits during which a scan was obtained lasted, on average, 126 minutes longer than those in which no scans were done. And, according to government statistics, spending on CT scanning increased from $975 million in 2000 to $2.17 billion in 2007, the researchers reported.

Researchers are still unsure what factors, aside from technological availability, are driving the additional scans. "We need to understand who is getting more scans, what the patient factors are, what the hospital institutional factors are," Korley says. "Then ultimately, we've got to figure out how we can take control of the problem." The bottom line for frontline trauma doctors in the meantime, he says, is to keep their Hippocratic obligations high. "We need to be careful since our goal is to do no harm," Korley says.

Scientific American is part of Springer Nature, which owns or has commercial relations with thousands of scientific publications (many of them can be found at www.springernature.com/us). Scientific American maintains a strict policy of editorial independence in reporting developments in science to our readers.